1. Field of the Invention
The present invention relates to a magnetic head, a head gimbal assembly, a hard disk drive, and a method of making the magnetic head.
2. Related Background Art
As hard disk drives have been increasing their recording densities, thin-film magnetic heads have been required to further improve their performances. As the thin-film magnetic heads, combined thin-film magnetic heads having a structure in which a magnetism detecting element such as a magnetoresistive (MR) element and a magnetic recording element such as electromagnetic coil element are laminated have been used widely, while these elements detect data signals of a magnetic disk which is a magnetic recording medium and write the data signals to the magnetic disk.
Known as a factor influencing the magnetism detecting performance of a thin-film magnetic head is a condition referred to as MR height which is the height of the magnetoresistive element in a direction perpendicular to its surface opposing the medium. This condition affects the magnitude of reproduced output of the magnetoresistive element, its asymmetry, and the like, and thus is required to be controlled precisely as designed.
The size of MR height is adjusted when cutting a wafer formed with a matrix of thin-film magnetic heads into rows called bars and lapping (polishing) a surface to be formed with the medium-opposing surface of each bar. For detecting the amount of lapping at the time of lapping, each bar is provided with a plurality of electric lapping guides (ELG, also known as resistance lapping guides or RLG).
Specifically, as disclosed in Japanese Patent Application Laid-Open No. 2003-91804, for example, a plurality of electric lapping guides are provided so as to face a surface to be formed with the medium-opposing surface of the bar. As this medium-opposing surface is lapped, the MR height decreases, whereby the electric lapping guides are also polished. This also reduces the height of the electric lapping guides in a direction perpendicular to the medium-opposing surface, whereby the electric resistance value of the electric lapping guides changes according to the amount of polishing. Therefore, measuring changes in the electric resistance value of the electric lapping guides at the time of lapping and terminating the lapping at a predetermined electric resistance value can carry out lapping such as to attain a predetermined MR height.
However, the conventional electric lapping guides are provided at positions distanced from the magnetoresistive element in the longitudinal direction of the bar, while the distance is large as compared with the size of the magnetoresistive element. Therefore, a certain degree of deviation may occur between the size of MR height calculated from the resistance value of the electric lapping guides and the actual size of MR height. In hard disk drives adapted to a high recording density in particular, margins in deviations tolerable in various characteristics of their constituents are so small that the degree of deviation in the size of MR height may become intolerable.
For preventing the above-mentioned deviation in MR height from occurring, a method measuring the resistance value of the magnetoresistive element itself at the time of lapping may be conceived. In a current-perpendicular-to-plane type element in which a sense current flows in a direction perpendicular to its surface of lamination, the distance between the upper and lower electrodes of the element is so short that the electrodes may instantaneously short-circuit under the influence of an abrasive agent or the like at the time of lapping, whereby the resistance value of the element may fluctuate greatly. When a tunneling magnetoresistive element is used as a magnetoresistive element, layers on the upper and lower sides of a barrier layer in the element may short-circuit similarly, whereby the resistance value of the element may further fluctuate. Consequently, the size of MR height has been hard to control precisely while measuring the resistance value of the magnetoresistive element itself at the time of lapping.
Therefore, it is an object of the present invention to provide a magnetic head in which the size of MR height is controlled precisely, a head gimbal assembly and a hard disk drive which are mounted with such a magnetic head, and a method of making a magnetic head in which the size of MR height is controlled precisely.